Hello Stefan!
Many thanks for your effort to improve SL setting. It is as
important as having good antenna.
:-)
I wrote your new parameters to my SL setting to try this one.
Gerhard, OE3GHB, was transmiting on 8970 las day, but I didn´t see
your signal. At first, I was surprised, but then I
realised, that my single-loop antenna was beamed to you. It means,
that it was in minimum receiving for Gerhard. I am going to turn it
at 217° and we will see. When I tested single-loop I noticed, there
was difference -20dB between direct beaming and +90° beaming on the
beacon in Germany. It is very much!
Dne 28.12.2010 16:39, Stefan Schäfer napsal(a):
Dear VLF,
In my 9th experiment, my signal was well received at 4X1RF in 2873
km
distance. Chris has recorded the whole procedure and sent me 4.5
GB on
a DVD as a registered letter (many thanks Chris!). I could
successfully
extract the 8970 Hz part in a 880 MB file. Then i re-processed
this
file several times in SpecLab, adjusting the FFT / Noiseblanker /
Clipper / Filter -settings. This recording is optimal for
re-processing
and looking for optimal settings since the SNR is relatively high
at
the beginning (up to 12 dB) and becomes lower (due to rising QRN)
at
the end. There is a longer section on 8970.00000 Hz and later the
message "CU" that is partly visible and partly lost in the QRN. So
the
goal was to make the whole message visible or at least as much as
possible.
The final improvement is rather marginal, probably not much more
than 2
dB. The pessimists will say its a pity that the SNR improvement is
not
more and the optimists will say its good that we obviously used
almost
perfect settings in the last tests ;-)
So, let me tell you about the results:
The left half of the attached picture shows the transmission as
received by using the current distributed USR files/settings (4.5
mHz
FFT, 60 s/pixel, 3 kHz band filter BW, 1 kHz filter slope, Clipper
threshold = 6 dB above avrg., Noise blanker set to 2 ms / 9 dB,
0.05
sec.). The right part shows the best SNR optimisation i achieved.
Of
course this is all a subjective decision, there is no strong
difference
but i find that the "CU", at least the "C" can be better
identified.
Reducing the FFT bandwidth should actually improve the SNR but the
readability decreases! There is not really an improvement between
4.5
mHz and 2.8 mHz, at least in this DFCW-600 transmission.
The SL settings of the best achievement are: 4.5 mHz FFT, 60
s/pixel,
Clipper threshold = 0 dB, Filter BW = 3 kHZ, Filter slope = 1 kHz,
Noiseblanker at 6 dB / 0.0003 sec ramp time, max. pulse width 0.05
sec.
Radio amateurs who are not operating in QRSS/DFCW mode may say
there is
no difference between the results ;-)
OK, the different is very good visible. Well done!
On 6470 Hz there was no significant improvement, even in longer
FFT
times. But my tests on that part are still not finished.
BTW, without using the SpecLab internal bandfilter, noiseblanker and
Clipper that signal would have been TOTALLY LOST!! There wouldn't
even
be the faintest trace of my signal!!
Yes, using all this tools is important, it is "big gun" agains a
noise.
I noticed, that Clipper red box indicace "C" continously. The
message says, that "signal is 0,0dB ABOVE clipping (A);
avrg=-5,9dB". Is it correct?
As a conclusion i would say that the current SL settings are well
suitable but a few dB SNR improvement could be achieved. Of course
this
depends on the kind of QRN/QRM and the antenna that is used. The
RX
stations who can receive my signal at 15 dB SNR or better will not
see
a significant difference but the new settings may be interesting
for
stations above 1000 km or below. Those who can set up the SL
paramaters
may try this. I will provide a new USR file for some RX stations
in
high distance before my next VLF experiment.
Any comments/hints are welcome.
When I was active on 137kHz, I had problems with noise and QRM as
well. My best SL configuration used function "reassigned diagram".
Using this function gave very good results. Would be usable on VLF
as well, or is it not suitable for QRSS600? I cann´t try it, becouse
I haven´t any control signal on 8970kHz.
73, Stefan/DK7FC
Have a nice last some days of 2010 year!
Lubos, OK2BVG
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